1. Field of the Invention
The present invention relates generally to an electric motor for use in a machine. More specifically, the present invention concerns a direct drive motor having an integral control system.
2. Discussion of the Prior Art
Those of ordinary skill in the art will appreciate that electric motors are often used in home appliances such as dishwashers and washing machines. In a washing machine, for instance, an electric motor may be used to cause rotation of the washer basket to agitate the clothing contained therein. Although a variety of motor component arrangements may be used, one known embodiment of an electric motor includes a stator positioned at least in part radially inside a rotor. An electric motor having such a configuration is commonly referred to as an outer rotor motor or external rotor motor, although other names may be used. In the case of a washing machine having an electric motor of this sort, the rotor is typically coupled to the washer basket, whereas the stator is fixed to a tub mounting hub that is coupled to a stationary washer outer tub. To avoid potential electrical shock of the user, the stator is mounted in such a manner that it is electrically isolated from the tub.
The stator of an outer rotor motor typically includes a core and a plurality of coils. Conventionally, the core takes a generally toroidal form and is composed of a ferromagnetic metal such as iron or steel. The core typically includes a plurality of teeth projecting radially outwardly and defining slots therebetween. The coils are formed by the winding of electrically conductive wire multiple times around each tooth to at least partially fill the slots. Electrical insulation is typically provided between the teeth and the coils.
Mounting of the outer rotor motor in the machine is conventionally accomplished through alignment of openings in the stator core with corresponding openings in the tub mounting hub, followed by insertion of a fastener through each aligned pair of openings. Such an approach is often inconvenient and expensive. For instance, traditional outer rotor motors are limited to a specific mounting arrangement incorporated into the core fabrication process. To use a conventional core in a different application requiring a different mounting arrangement, the core fabrication process must be varied (e.g., the lamination die for a laminated stator core must be re-machined). Furthermore, the metal core must be large enough to house the mounting openings, making the core heavy and expensive. Even further, the increased number of components in the machine-motor system, including fasteners such as bolts or screws, slows the assembly process and increases the risk that a component necessary for assembly will be misplaced.
A motor drive or control board assembly is typically provided to control the electric motor. Conventionally, the control board assembly is located remotely from the motor and is connected thereto by a wiring harness. The control board assembly is additionally connected by lead wires to a machine control interface that is typically located on the front of the machine for ease of user access. The extensive wiring required for such a configuration adds to the expense of the machine and also increases the potential for electromagnetic interference problems to arise. The multiple connections required increase the risk that a faulty connection will hinder performance. Furthermore, since the standard control board assembly position is in a water-prone area, a dripshield housing must typically be provided to protect the control board assembly from encroachment of water or other liquids. Finally, the high number of components and assembly steps increases the time required for assembly and, in turn, the total cost of the machine.